Pneumatic springs, commonly referred to as air springs and/or air struts, have been used with motor vehicles for a number of years to provide cushioning between the movable parts of the vehicle, primarily to absorb shock loads impressed on the vehicle axles by the wheel striking an object in the road or falling into a depression. These air springs usually consist of a flexible elastomeric sleeve or bellows containing a supply of compressed air having one open end connected to an end plate with the other open end sealingly connected to a piston which extends into the fluid chamber. The piston causes compression and expansion of the fluid within the chamber as the vehicle experiences the road shock to absorb the shock. These air springs also maintain a predetermined spacing between the vehicle components to which they are attached and are generally mounted on the vehicle axles to support the body portion of the vehicle from the axles. In addition, the air springs maintain the vehicle body at a predetermined level above the vehicle axle in order for the air spring to be able to withstand the road shock loads exerted thereon by providing sufficient jounce or collapse movement and rebound or expended movement of the air spring without damaging the flexible sleeve and connected end members. It is also desirable to be able to instantaneously regulate the amount of fluid in the air spring to compensate for shocks exerted on the air spring by road surface variations. The term air spring as used herein also includes devices having an air or fluid strut incorporated with the flexible sleeve for dampening the road inputs.
In order for the air spring to perform satisfactorily it is necessary that the proper amount of pressurized fluid be contained within the flexible sleeve to insure the correct axial spacing between the end members of the air spring and to maintain predetermined damping characteristics while the air spring is encountering road shocks. Also, most vehicles will be equipped with at least two air springs spaced from each other and mounted adjacent the ends of each of the vehicle axles to insure leveling of the vehicle body. Therefore it is important that the correct amount of pressurized fluid, generally air, be maintained in each of the air springs to enable the air springs to provide their desired shock absorbing feature in addition to maintaining the vehicle body level with respect to the axle.
Certain of these air springs are provided with a sealed flexible sleeve whereby the pressurized fluid remains trapped within the chamber whereas other air springs are provided with pressurized air control systems for supplying make up air into the air chamber and/or exhausting air therefrom in order to maintain the desired amount of pressurized air in the chamber.
Various types of automatic control systems have been devised for use with air springs to maintain the desired spacing between the end members thereof. Certain systems use the "Hall effect" or magnetic reed switches whereas others use light sensors and photodetectors for detecting the spacing between the end members. Still other air springs use contact switches mounted either externally or internally of the pressurized fluid chamber for determining the separation of the end members and for introducing or exhausting air into and from the fluid chamber in response to signals received from such detecting mechanism.
Many of these prior art air spring systems have the disadvantage of using component parts located exteriorly of the air spring, either mounted on the air spring or vehicle, or a combination of both, which subjects the components to the harsh road environment to which a vehicle is subjected. Whereas, the components of other systems mechanically engage each other ultimately requiring replacement or repair due to the mechanical interaction of these control system components.
U.S. Pat. No. 3,150,867 discloses a self-contained shock absorber and self-leveling device which through a sequence of valving uses the pumping action of the shock absorber to jack up the frame of the vehicle to a predetermined height.
U.S. Pat. Nos. 3,269,685 and 4,391,452 disclose vehicle leveling systems which use photoelectric cells as a concontact height detecting device.
U.S. Pat. No. 2,743,429 discloses the use of an ultrasonic transducer to determine the relative distance of two objects when one of the objects is in motion with respect to the other in which the distance information energizes a servo system to move one of the objects.
U.S. Pat. No. 4,518,169 discloses an ultrasonic height sensing device which provides height signal information to a feedback system to automatically adjust vehicle height. However this system measures the height using ultrasonic transducers mounted on the vehicle body whereby such transducers would be subject to the harsh environment to which a vehicle is constantly exposed.
U.S. Pat. No. 4,543,649 discloses an ultrasonic transducer for determining the relative position of a piston in a rigid housing in combination with a feedback control system for compensating for any displacement of the piston. The ultrasonic transducer insures that the piston is maintained in a relative position within the housing.
Although certain prior art devices use ultrasonic transducers for adjusting the height or spacing between components, none of said prior art devices disclose or suggest the use of such an ultrasonic transducer which is concealed within the body of an air spring or shock absorber in connection with a vehicle air spring system as does our invention described in detail below and shown in the drawings.
Therefore the need exists for an air spring system in which certain of the principle components or detecting components are located within the air suspension element or fluid pressure chamber to determine and maintain the correct axial spacing of the end members of the suspension system to eliminate contacting mechanical height sensing components heretofore used in such systems.